1. Field of the Invention
The present invention relates generally to the operation of a manual transmission in a motor vehicle. More particularly, the invention is directed to a system and method of automatically matching engine speed to vehicle speed of a motor vehicle while an operator shifts a manual transmission in the vehicle.
2. Background
Conventional motor vehicles, such as automobiles, typically have engines that produce low torque over a fairly narrow range of high engine speeds. However, high torque and a broad range of lower speeds at the drive wheels are required to move an automobile. Thus, the high-speed low engine torque is converted to a low-speed high wheel torque suitable for a variety of driving conditions by a multiple-speed drivetrain in the automobile. A variable-speed-ratio transmission and a pair of final drive gears are the typical elements in such a conventional drivetrain. A manual transmission is one major type of variable-speed-ratio transmission, wherein, as the name implies, the automobile operator must select from several speed ratios using a manual gear selector. The gear selector may be a hand lever that resembles a stick, as typically found in cars and trucks, or a foot pedal, as typically found on motorcycles.
A conventional manual transmission typically includes an input shaft driven by the engine, a layshaft driven by the input shaft, and one or more mainshafts driven by the layshaft. Mounted to the layshaft and mainshafts are several pairs of gears of different ratios in constant mesh. The input gear of each pair is solidly attached to the layshaft. These pairs of gears provide the forward speed ratios. A set of three gears driven by the layshaft and selectively driving the mainshaft provides a reverse speed ratio. The output gear in each pair is free to rotate about the mainshaft. A speed ratio, or “gear”, is selected by locking one of the output gears to the mainshaft with toothed collars that are positioned by the gear selector. One gear is “higher” than another if the numeric ratio of input speed to mainshaft speed of the higher gear is lower relative to the lower gear. The gears are referenced in numeric sequence. The lowest is first gear, the next-lowest is second gear, and so on for all forward gears. Motor vehicles typically have multiple gears. For example, cars, light trucks, and motorcycles with manual transmissions generally have five or six forward gears.
Manual transmissions in motor vehicles may be synchronized, as in cars and lighter trucks, or unsynchronized, as in motorcycles, race cars, and heavy trucks. As a gear in a synchronized manual transmission is selected, an additional component called a synchronizer introduces friction between the gear and the engine output shaft in order to bring the gear speed to parity with the mainshaft speed before the collar is locked.
A clutch assembly (hereinafter, “clutch”) is used to separate the engine and transmission input shaft while gears are changed. The operator releases the clutch by applying force to a foot pedal, usually found in cars and trucks, or to a hand lever, usually found on motorcycles. The clutch typically includes a flywheel and a pressure plate attached to the engine and a clutch plate attached to the transmission input shaft. The clutch is engaged by a spring that forces the pressure plate against the clutch plate, which in turn forces the clutch plate against the flywheel. Friction between the flywheel and clutch plate allows engine torque to flow to the rest of the drivetrain. The clutch is disengaged by a throw-out bearing that works against the spring to pull the pressure plate away from the clutch plate, eliminating the friction between the flywheel and the flow of engine torque to the transmission and effectively breaking the flow of torque to the drivetrain.
Conventionally, the process of shifting gears while the vehicle is in motion is as follows. The vehicle operator may initiate an upshift, i.e., a change from a lower gear to a higher gear, by decreasing the throttle input (e.g., releasing the gas pedal in a car) to reduce engine torque and disengaging the clutch (e.g., applying force to the clutch pedal in the car) to reduce the flow of engine torque to the drivetrain. Next, the operator moves the gear selector to the neutral position. Then, the operator further decreases the throttle input to reduce engine speed to match the lower transmission input shaft speed that is to result from the upshift. The lower transmission input shaft speed may be obtained by multiplying the rotational speed of the drive wheels, the final drive ratio, and the next transmission gear. The operator continues to move the gear selector from the neutral position to the position of the higher gear, i.e., the lower speed ratio, causing the collars to lock the newly selected gear to the output shaft. Finally, the operator reengages the clutch (e.g., releasing the clutch pedal in the car).
The operator may initiate a downshift, i.e., change from a higher gear to a lower gear, with one of two procedures. In the more frequently used procedure, the operator initiates the downshift by again decreasing the throttle input to reduce engine torque and disengaging the clutch to reduce the flow of engine torque to the drivetrain. Next, the operator moves the gear selector to the neutral position. Then, the operator increases the throttle input to increase engine speed to match the higher transmission input shaft speed that is to result from the downshift. Again, the higher transmission input shaft speed may be obtained by multiplying the rotational speed of the drive wheels, the final drive ratio, and the next transmission gear. The operator continues to move the gear selector from the neutral position to the position of the lower gear, i.e., the higher speed ratio, causing the collars to lock the newly selected gear to the output shaft. Finally, the operator reengages the clutch. This method is known as “single-clutching”, since the clutch is disengaged once per shift.
The second method of downshifting requires the clutch to be disengaged twice and is therefore known as “double-clutching” or “double-declutching.” The operator initiates the downshift by decreasing throttle input to reduce engine torque and disengaging the clutch to break the flow of engine torque to the drivetrain. Next, the operator increases the throttle input to increase engine speed to match the higher transmission input shaft speed that is to result from the downshift. Again, the input shaft speed is obtained by multiplying the rotational speed of the drive wheels, the final drive ratio, and the next transmission gear. At the same time, the operator shifts to neutral, reengages the clutch briefly and then disengages the clutch again. The engine speed that is needed to smoothly engage the clutch, once the shift is completed, is also the transmission input shaft speed that matches the output gear speed and the mainshaft speed in order to smoothly lock the gear collars. The engagement of the clutch with the transmission in neutral and with higher engine speed raises the speed of the output gear before it is locked to the output shaft. Next, the operator moves the gear selector from the neutral position to the position of the lower gear, and the clutch is released again. Compared to the single-clutch procedure, the double-clutch procedure eases the process of locking the collars of the newly selected gear to the output shaft.